Communication method and apparatus



April 14, 1964 R. w. zlEMER COMMUNICATION METHOD AND APPARATUS 2 Shets-Sheei 1 Fil'ed April 5, 1960 Amas/#595 Apnl 14, 1964 R. w. zu-:MER 3,128,965

COMMUNICATION METHOD AND APPARATUS I Filed April 5, 1960 2 She-ets-Sheet 2 United States Patent O M 3,128,95 COMMUNCATQN METHOE AND APPARATUS Richard W. Ziemer, Gardena, Calif., assigner to Space Technology Laboratories, Inc., Los Angeies, Calif., a corporation of Delaware Filed Apr. 5, 1960, Ser. No. 20,685 11 Claims. (Cl. 244-14) This invention relates to telemetry and radio cornmunication, and has particular reference to a method for communicating radio waves through a layer of ionized gas which tends to attenuate the waves. At the present time the method is particularly applicable to iiight vehicles traveling at hypersonic speeds through the earths atmosphere.

The presence of an ionized gas layer adjacent one of two stations will adversely affect and, depending upon the degree of ionization, will totally block radio wave communication between the stations. For example, a serious problem encountered during the atmospheric reentry of a missile is the black out of telemetry and radio transmission because of a -shock-Wave-induced layer of ionized gas effectively surrounding the missile during a part of its trajectory. The ionized gas layer affects the radiation pattern from the missile antennas by attenuation and distortion, and by detuning the antennas. Further, the presence of the hot ionized gas layer reduces the power level at which radio frequency breakdown occurs adjacent the antennas.

In accordance with the present invention, a solution to the problem of communicating radio waves through a layer of ionized gas is provided by directing a fluid stream which is relatively transparent to the radio waves into the layer of ionized gas so as to produce a region in the ionized gas layer which is relatively transparent to the radio waves. While the iluid stream continues, radio waves are communicated through the resulting transparent region of the ionized gas layer, preferably by means including an antenna located adjacent to or in the duid stream and having a significant radiation pattern in the affected regions of the stream.

in accordance with one embodiment, where the station adjacent the ionized gas layer is a flight vehicle moving through the atmosphere, the iluid stream is directed forward from a stagnation point on the vehicle, preferably at a suioient ow rate to penetrate the preceding bow shock wave. The iiuid discharge may be triggered by means of a radio signal Ifrom a ground station, where adequate warning of the occurrence of the condition is available from radar tracking, or Ifrom observation of the attenuation of the normal radio wave transmission from the vehicle. The process does not require excessive larnounts of uid because the iiuid discharge may be maintained only during those periods ywhen conditions of altitude and speed combine to cause an ionized gas layer suficient to seriously interfere with normal communication. For present day re-entry vehicles, this period of time is measured in seconds.

There are many non-conductive lluids both gaseous and liquid that may be employed to create the relatively transparent region or window in the layer. Preferably, the Huid used should have a relatively high ionization potential. Examples of suitable fluids are air, hydrogen, helium, neon, uorine and water.

The process is explained in more detail with reference to the accompanying drawings, in which:

FIG. 1 is a fragmentary schematic diagram of a iiight vehicle re-entering the ear-ths atmosphere at hypersonic speed, with suitable apparatus incorporated in the vehicle for carrying out the process;

FlG. 2 is an enlarged fragmentary View of the area 3,128,965 Patented Apr. 14, 1964 ICC surrounding the nose of a vehicle during the iluid discharge, and illustrates an antenna system slightly different from that shown in FIG. l; and,

BIG. 3 is a fragmentary View of another embodiment of the present invention.

Referring to FIG. 1, a flight vehicle d0 re-entering the earths atmosphere at lhypersonic speed generates a bow shock wave 12 which precedes the vehicle. The movement of the undisturbed atmosphere relative to the vehicle is indicated by the vertical column of arrows. As this oncoming air meets the bow shock wave it is compressed and decelerated with resulting heating, to form a hot gaseous layer 14- between the shock Wave and the vehicle, called the shock layer, in which the gas ilows in an oblique pattern approximately as 4indicated by the arrows. Compression and heating are greatest, hence the degree of thermal ionization is greatest, in the region 16 near the stagnation point, the foremost point on the nose of the vehicle, opposite which the velocity vector of the undisturbed atmosphere is most nearly normal to the bow shock wave. In this region, which may be called the stagnation region, the velocity of gas relative to the vehicle .is at a minimum. The temperature decreases toward the rear of the vehicle, unless other obstructions such as protruding fins or antennas produce an increase.

The temperature of the gases in the shock layer is a function of the speed Aand altitude of the vehicle, and under suitable conditions will exceed the threshold for thermal ionization of air, about 3,000 degrees Kelvin. As the vehicle descends into the atmosphere, the air temperature in the shock layer may rise to several thousand degrees Kelvin, causing the air in this region to become thermally ionized, hence electrically conducting. The thermally produced ions, once created, tend to persist. The result is an enveloping layer of ionized gases, a socalled plasma sheath, which extends back over the body of the missile and subsequently forms a turbulent wake. Observation of re-entry vehicles has shown that when the vehicle velocity approaches 10,0010 feet per second (about Mach l0) at altitudes below 300,010() feet, the plasma sheath is formed around the vehicle. At greater speeds, say Mach 16 to 20, the ionization becomes so severe as to disable the vehicle both as a sending and as a receiving station. The problem is not solved by increasing the power at which the vehicle antennas are driven because of the limiting effect of radio frequency breakdown of the gas.

As indicated in FIG. 1, the vehicle 10 normally has one or more transmitters and receivers 13 coupled to slot type antennas flush mounted at positions spaced around the body of the vehicle. .A typical side lslot antenna 2u is shown. The enveloping layer of ionized gas detunes the slot antennas, and attenuates and distorts the antenna radiation pattern.

To communicate through the plasma sheath, the fluid discharge is initiated, Depending upon the speed and altitude of the vehicle as determined from radar tracking at a ground station, or depending upon observations of attenuation of signals received from the flight vehicle at a ground station, an adequate warning is available to send a triggering signal to a radio actuated control 22 in the vehicle, which initiates the discharge of a suitable fluid contained in a resenvoir 214. If desired, the control 22 may be triggered automatically by incorporating equipment (not shown) in the vehicle yfor sensing the condition.

The radio actuated control 22 activates a fluid control system exempliiied in FIG. l by a pump 25 located serially in a discharge line 26 from the fluid reservoir, and shut-oif valve such as a solenoid operated shut-off valve 2S. A pressure regulating valve 3i) is disposed serially with the pump 2S and the shut-off valve 2f in the discharge line. The discharge line 2-5 runs to the inlet 3d of a jet orifice 36 disposed coaxially with the vehicle. The jet orifice, at its forward end, opens through the apex of the nose of the vehicle. A radiative source such as a slot antenna 33 is mounted near the end of the jet orifice, and is oriented so that its maximum radiation field lies approximately along the axis thereof.

The radio actuated control 22 triggers the actuation of the pump 25 and the opening of the shut-off valve 23, whereupon fluid from the reservoir 24, at a pressure regulated by the regulator 3i), is discharged out the jet orifice 36 into the stagnation region 16, making this region relatively transparent to radio waves. The discharge continues so long as there is a supply of fluid and so long as the pump is powered and the shut-off valve is held open.

During the fluid discharge, radio wave communication through the relatively transparent region is facilitated by the slot antenna 33, because its location and orientation relative to the fluid stream causes a maximum of its radiation pattern to lie approximately along the stream and permits it to operate at a relatively high power level without radio frequency breakdown. rThe slot antenna 38 may be operated concurrently with other slot antennas 2t) of the vehicle during the fluid discharge as well as at other times. However, if desired, the signal from the control 22 may be employed to switch couple the slot antenna 38 to the transmitters and receivers 18 only during those times the fluid discharge is in progress.

Referring now to FIG. 2, there is shown a slightly different antenna system including an open end waveguide tube 38a having an exciting probe 39 positioned in front of a reecting grid arrangement 41. Such an antenna system is well known in the present state of the waveguide art and need not be described in detail herein. However, this arrangement when used in connection with the present invention has the advantage of allowing the fluid to flow through a straight duct system rather than the curved one illustrated by way of example in FG. 1. However, when a curved duct system is used, as shown in FIG. l, additional types of antenna arrangements may be utilized.

In accordance with the FIG. 2 embodiment of the present invention as well as the one depicted in FIG. 1, a fluid discharge directed upstream from the stagnation region produces a relatively transparent region in the shock layer by penetrating and by diluting the ionized gases and by reducing the temperature. The transparent region is defined approximately by a central column of unmixed fluid 4f) and a turbulent mixing zone 42, Ion formation is retarded and recombination is encouraged by a lowering of the temperature in this region as a result of the presence of the fluid, To this end, the disr charged fluid should be at a relatively low temperature, and the employment of a liquid has an added advantage of utilizing the heat of vaporization of the liquid for cooling the region.

The fluid discharge may be maintained at an adequate flow rate to penetrate the ionized shock layer and the normal bow shock wave, thereby to create a weaker shock wave 44 having a near conical shape. Since the angle of the conical shock wave 44 relative to the free stream velocity vector is much greater on the average than on the corresponding portion of an undisturbed bow shock wave, the resulting temperature rise for the air passing through it is less. While a penetration of the bow shock wave by the fluid stream is desirable, it is equally clear that any significant fluid discharge into the stagnation region will decrease the ion density and hence make this region, as well as the region adjacent the side slot antennas, more transparent to radio waves.

Referring now to FIG. 3, there is shown a schematic fragmentary View of the vehicle l@ having one or more transmitters and receivers 18 connected to a plurality of circumferentially disposed side slot antennas 2t) for receiving and sending various types of signal information. In accordance with this embodiment of the present invention, the jet orifice 36 has been omitted and a plurality of jet orifices 36a are positioned upstream of the side slot antennas Ztl to emit fluid into the plasma stream of the hot gaseous layer 14. Thus regions of unionized fluid lila are created. When using a jet stream emission at one side of the vehicle it is often desirable to balance this with one or more jets about the circumference of the vehicle l@ so that no tumbling thrust is created. if the jet stream from the nozzle of the jet orifices 36a is carefully positioned to create a thrust passing through the center of gravity of the vehicle, a single jet stream may be used without creating tumbling.

Usually it will be preferred that the nozzle configuration of the jet orifice 36a is of a type allowing supersonic flow into the hot gaseous layer 14 so that the window created by the emitted gas penetrates substantially through this hot gaseous layer. Moreover, the use of the jet orifices 36a to create a net thrust on a line slightly in front of the center of gravity may be utilized by selectively causing unequal fluid ejection to control the vector of flight of the vehicle 1t) for providing trajectory corrections on the order of half a mile or more. A selective fluid controller valve i6 is energized in accordance wtih signal information from the radio actuated control 22.

Although several embodiments of the present invention have been described in some detail above, it is recognized that there are many relevant phenomena which must be considered to provide a most eective window in the plasma sheath of the hot gaseous layer 14. For instance, the electromagnetic energy radiated by antennas tends to ionize adjacent gaseous regions as a function of the power level of operation of the antenna with any ions in the immediate vicinity of the antenna acting somewhat like catalysts to increase this ionization problem often referred to as radio frequency breakdown. With the occurrence of the plasma sheath of the hot gaseous layer 14 during re-entry of the vehicle 10, it may be expected that some ions will be in the region of the antenna wave fields despite the provision of cool fluid jets. However, when the fluid of the jet is carefully selected as a function of the frequency of radiation, it is feasible to reduce this problem to a minimum. It is contemplated that for most of the antenna systems or other radiation sources of the type likely to be used, such as slot antennas Ztl, the use of gases having high ionization potential as the emitted fluid will be most effective to minimize or eliminate radio frequency breakdown in the hot gaseous layer. As mentioned above, these gases will be of the type exemplifed by neon, helium, hydrogen, or fluorine. It is recognized that many fine powder materials, when sulficiently agitated, as by high velocity air streams, may be treated as fluids, and it is contemplated that some of these solid particle fluids may be advantageously employed in the present invention.

I claim:

1. In communicating radio waves between first and second stations, effectively surrounding the first of which is a layer of ionized gas that tends to attenuate the radio waves, the method comprising directing a fluid stream which is relatively transparent to the radio waves into the layer of ionized gas from the first station so as to provide a region in the ionized gas layer which is relatively transparent to the radio waves, and communicating between the stations with radio waves through the relatively transparent region by means including an antenna located at the first station adjacent the directed fluid stream, said antenna having a maximum of its radiation pattern directed along the fluid stream.

2. The method of claim 1 wherein the first station is a flight vehicle moving through the atmosphere at hypersonic speed and wherein the fluid stream is directed in the direction of movement of the vehicle from a stagnation point on the vehicle.

3. In communicating radio waves between first and second stations, the first of which is a fiight vehicle moving at hypersonic speed through the atmosphere and effectively surrounded by an attenuating layer of thermally ionized gas consequent upon a bow shock wave preceding the vehicle, the method comprising discharging a fiuid stream that is relatively transparent to the radio waves into the ionized gas layer to produce therein a region which is relatively transparent to the radio waves, the fiuid stream being directed from a stagnation point on the vehicle and approximately in the direction of movement of the vehicle, and communicating radio waves between the stations through the relatively transparent region in the ionized gas layer by means including an antenna on the flight vehicle which is located adjacent the fluid stream and has a maximum of its radiation pattern directed along the iiuid stream.

4. The method of claim 3 wherein the fluid stream is passed through the bow shock wave to create a protruding shock front whereon the angle of the shock wave of the protruberance relative to the free stream velocity vector is greater on the average than it was originally on the corresponding part of the bow shock wave.

5. The method of claim 3 wherein the discharged fluid is at a relatively low temperature compared to the ionized gas so as to retard ion formation and encourage recombination by reducing the temperature inthe region.

6. The method of claim 5 wherein the fluid is discharged in liquid form to take advantage of the heat of Vapor-ization of the liquid in cooling the ionized gas.

7. The method of claim 3 wherein at least a portion of the discharge iiuid has a high ionization potential compared to the ionized gas so as to inhibit ion formation in the region of fluid discharge.

8. In communicating radio waves between first and second stations, the first of which is a moving fiight vehicle capable of moving through the atmosphere at a speed and altitude where the gases in the shock layer around the vehicle become thermally ionized, the method comprising sensing the approach of the ionized condition of said shock layer, triggering the discharge of a fluid stream which is relatively transparent to radio waves into the ionized shock layer, the fluid stream being directed into the shock layer forward of an antenna of the vehicle to create a region transparent to radio waves, and communicating between the stations by passing radio waves through said transparent region by means including the antenna.

9. A radio communication antenna system arranged for transmitting signal information through a relatively thin, ionized hot gaseous layer of the type which will attenuate signal information wave fields and which frequently is encountered during high speed atmospheric travel such as during re-entry of a satellite-like vehicle, comprising:

an electromagnetic radiation source positioned to propagate a signal information wave field from the vehicle; and

means for injecting a fluid into the ionized hot gaseous layer in a region creating an opening for at least an effective portion of the wave field during the occurrence of severe ionization.

10. A radio communication antenna system arranged for transmitting signal information through a relatively thin, ionized hot gaseous layer of the type which will attenuate signal information wave fields and which fre quently is encountered during high speed atmospheric travel such as during re-entry of a satellite-like vehicle, comprising:

a vehicle having defined in the surface thereof a plurality of circumferential positioned uid jet orifices; an electromagnetic radiation source positioned downstream of each of the orifices to propagate a signal information wave field from the vehicle; and

valve means for selectively ejecting a fluid into the ionized hot gaseous layer through at least one of the orifices to create a transparent region for substantial portions of the wave field of at least one of said sources during the occurrence of severe ionization. l1. A radio communication antenna system arranged for transmitting signal information through a relatively thin, ionized hot gaseous layer of the type which will attenuate signal information wave fields and which frequently is encountered during high speed atmospheric travel such as during re-entry of a satellite-like vehicle, comprising:

a vehicle having defined in the surface thereof a plurality of circumferentially positioned fluid jet orifices; an electromagnetic radiation source positioned downstream of each of the orifices to propagate a signal information wave field from the vehicle;

valve means for selectively ejecting a fluid into the ionized hot gaseous layer through at least one of the orifices to create a transparent region for substantial portions of the wave field of at least one of said sources during the occurrence of severe ionization; and

control means for regulating the operation of said valve means in accordance with the attitude of the vehicle to thus provide trajectory corrections.

References Cited in the file of this patent Homic et al.: Communicating With The Hypersonic Vehicle, Astronautics, vol. 4, No. 3, March 1959, pp. 36, 37, 92, 94, 96 and 98. (Copy in Scientific Library.) 

1. IN COMMUNICATING RADIO WAVES BETWEEN FIRST AND SECOND STATIONS, EFFECTIVELY SURROUNDING THE FIRST OF WHICH IS A LAYER OF IONIZED GAS THAT TENDS TO ATTENUATE THE RADIO WAVES, THE METHOD COMPRISING DIRECTING A FLUID STREAM WHICH IS RELATIVELY TRANSPARENT TO THE RADIO WAVES INTO THE LAYER OF IONIZED GAS FROM THE FIRST STATION SO AS TO PROVIDE A REGION IN THE IONIZED GAS LAYER WHICH IS RELATIVELY TRANSPARENT TO THE RADIO WAVES, AND COMMUNICATING BETWEEN THE STATIONS WITH RADIO WAVES THROUGH THE RELATIVELY TRANSPARENT REGION BY MEANS INCLUDING AN ANTENNA LOCATED AT THE FIRST STATION ADJACENT THE DIRECTED FLUID STREAM, SAID ANTENNA HAVING A MAXIMUM OF ITS RADIATION PATTERN DIRECTED ALONG THE FLUID STREAM. 